The present invention relates to a format of an optical disc, and more particularly to a rewritable optical disc.
Optical discs are presently very widely used as a media for recording software such as picture, sound and computer data. In particular, lately, there is an increasing demand for enhancing optical disc recording density, and the development of an optical disc format suitable to meet such a demand is therefore highly desirable.
A format of an existing xe2x80x9c130 mm rewritable optical discxe2x80x9d is described below.
The format of the 130 mm rewritable optical disc is specified in JIS X 6271. The format includes type A format in which a continuous groove is spirally formed on a disc, and the lands between the grooves are used as tracks for recording signals, and type B format, in which samples marks are formed on a disc, and tracking is controlled by a sample servo system.
The tracks for recording information data in the type A format are wobble (i.e., slight vibration)-free tracks, and information data is recorded only in the lands (between grooves). In type A format, a standard user data format in the case of user data capacity of 512 bytes is shown in FIG. 14. Numerals shown in the diagram refer to the number of bytes (B) to be distributed in each signal. In the user bytes of 512 B, correction codes, re-synchronization bytes and control bytes are added, and the data field has a capacity of 650 B. In the sector for recording signals in the data field, it is necessary to add a sector mark (SM) designating the beginning of the sector, a VFO field for synchronizing with clock reproduction, an ID field showing the sector address, a pre-recorded address field such as an address mark (AM) showing the beginning of the ID field, an offset detection field (ODF) for rewriting the data, and including ALPC used in inspection of laser output, a buffer field of 15 B used to preclude overlap with the succeeding sector, and other fields, as necessary. As a is result, the total sector capacity is 746 B. For the user data capacity of 512 B, the buffer field is 15 B, and there is a redundancy of about 2.9%. For a further larger capacity, it is desired to curtail the redundancy as much as possible.
In such a conventional rewritable optical disc, when recording information on a wobble-free guide track, usually, the information is processed by using a fixed clock associated with the optical disc device. However, due to effects of rotation fluctuations or eccentricity when recording and reproducing information in an optical disc, the actual sector length may, in fact, deviate from the ideal sector length, thereby causing an increase or decrease in the number of clock pulses counted by a fixed clock. For example, if the number of clock pulses is decreased, the information cannot be recorded completely within the sector and may overflow into the next sector. Hence, the buffer field is provided by considering preliminarily a clock decrement, so that the sector length is extended. By the corresponding portion, therefore, the redundancy increases, and user data capacity is sacrificed.
Besides, when recording data continuous in time, such as video data and audio data, in the conventional method of recording after once confirming the address of the sector, if the sector address can not be confirmed, it takes time to confirm the address again and record, and continuous data can not be recorded. In another method of recording data wherein the sector address is predicted from a previous address without reconfirming the sector address, errors are accumulated when counting the sector length by a fixed clock, and the counting deviation increases.
In particular, in the intermediate address method in the land-groove recording system having a possibility of decline of address detection precision, it was possible that the above problem of continuous recording of video data and audio data could be even more serious.
Further, in the future, if there are optical discs having several different data capacities with narrower track pitch in the rewritable field, the format of the optical discs must be such that they are all compatible with each other.
The present invention is devised in light of the above-described problems, and it is hence an object thereof to provide an optical disc having such a format as to obtain easily a recording and reproducing apparatus of high reliability capable of controlling tracking or stably generating a clock, and an apparatus for stably manufacturing such optical discs.
Further, in an optical disc containing both a ROM field (including read-in area) and a rewritable field, it is an object of the present invention to provide an optical disc format capable of generating a stable clock for processing information data at the beginning of the rewritable field, and recording information data accurately. It is also an object to present a format capable of easily achieving compatibility of several types of optical discs differing in their respective data capacities.
To achieve these and other objects, a first aspect of the optical disc of the invention relates to an optical disc having an ID field, an information recording field, and an information unrecorded field between the ID field and the information recording field, formed in every one of a plurality of sectors composed on a guide track, in which the ID field contains a plurality of address information, and is recorded in convex and concave signals, and composed of two sets deviated by about xc2xd track pitch each in the direction of internal or external circumferential track adjacent to the guide track, the information recording field is composed of grooves and lands (between grooves) wobbling (oscillating slightly) at a single frequency in the radial direction, and the grooves and lands are changed over in every turn of the guide track.
A second aspect of the optical disc of the invention relates to an optical disc wherein when the information contained in one period of wobble is w bits, the information unrecorded field between the ID field and information recording field has a length of w/10 bits or more and/or w bits or less.
A third aspect of the optical disc of the invention relates to an optical disc in which the information to be recorded in the information recording field begins with a specific phase of wobble frequency.
A fourth aspect of the optical disc of the invention relates to an optical disc in which the sector has a length of an integer multiple of the wobble frequency, and an integer number of the sectors are contained in every turn of the guide track.
A fifth aspect of the optical disc of the invention relates to an optical disc having an ID field and an information recording field, formed in every one of a plurality of sectors composed on a guide track, in which the ID field contains a plurality of address information, and is recorded in convex and concave signals, the information recording field is composed of grooves and lands (between grooves) wobbling (oscillating slightly) at a single frequency in the radial direction, the grooves and lands are changed over in every turn of the guide track, the sector has a length of an integer multiple of the wobble period, an integer number of the sectors are contained in every turn of the guide track, and the initial phase of every turn of the guide track of the wobble is within xc2x1n bits of information bits, the final phase within xc2x1m bits, and their relation is n  less than =m (n, m being natural numbers).
A first aspect of the optical disc manufacturing apparatus of the invention comprises ID signal generating means for generating a signal for the ID field, specified signal generating means for generating a signal in portions other than the ID field, wobble signal generating means for generating a wobble signal at a single frequency, timing signal generating means for providing a gate signal of specified timing, first signal selecting means for selecting either the ID signal or the specified signal, deflection signal generating means for issuing a deflection signal for deviating the ID field by about xc2xd track pitch each to the inner circumferential side and outer circumferential side of two sets, second signal selecting means for selecting either the wobble signal or the deflection signal, deflecting means for receiving the output of the second signal selecting means and deflecting the light spot, and reset means for resetting the phase of the wobble signal in every revolution of the optical disc.
A second aspect of the optical disc manufacturing apparatus of the invention comprises first signal selecting means for making valid either the ID signal or the specified signal, light spot diameter adjusting means for changing the size of a light spot by receiving the timing signal, on/off control means for making valid/invalid the wobble signal by the timing signal, deflecting means for receiving the output of the on/off control means and deflecting the light spot, and reset means for resetting the phase of the wobble signal in every revolution of the optical disc.
A sixth aspect of the optical disc of the invention relates to an optical disc composed of coexistence of a ROM field having information with a length of at least one track formed in convex and concave pit rows, and a rewritable field with a length of at least one track, in which an information unrecorded field with a length of at least one track is recorded is formed between the ROM field and the rewritable field, the rewritable field has a spiral or concentric guide track wobble in the radial direction, the ROM field is formed of spiral or concentric convex and concave pit rows, and a part or a whole field at the rewritable field side of the information unrecorded field has a transition field having a spiral or concentric guide track wobbling in the radial direction continuously or intermittently.
A seventh aspect of the optical disc of the invention relates to an optical disc in which the ROM field is a read-in field, and the track pitch To of the ROM field and the track pitch Tw of the rewritable field have the following relationship: To  greater than =Tw.